U.S. patent application number 11/387219 was filed with the patent office on 2007-01-25 for alloy composition for lithium ion batteries.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Leif Christensen, Mark N. Obrovac.
Application Number | 20070020522 11/387219 |
Document ID | / |
Family ID | 37461353 |
Filed Date | 2007-01-25 |
United States Patent
Application |
20070020522 |
Kind Code |
A1 |
Obrovac; Mark N. ; et
al. |
January 25, 2007 |
Alloy composition for lithium ion batteries
Abstract
Alloy compositions, lithium ion batteries, and methods of making
lithium ion batteries are described. The lithium ion batteries have
anodes that contain an alloy composition that includes a) silicon,
b) aluminum, c) transition metal, d) tin, e) indium, and f) a sixth
element that contains yttrium, a lanthanide element, an actinide
element, or a combination thereof. The alloy composition is a
mixture of an amorphous phase that includes silicon and a
crystalline phase that includes an intermetallic compound of 1)
tin, 2) indium, and 3) the sixth element.
Inventors: |
Obrovac; Mark N.; (St. Paul,
MN) ; Christensen; Leif; (St. Paul, MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
37461353 |
Appl. No.: |
11/387219 |
Filed: |
March 23, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60702244 |
Jul 25, 2005 |
|
|
|
Current U.S.
Class: |
429/218.1 ;
420/589; 429/217; 429/231.95 |
Current CPC
Class: |
H01M 4/38 20130101; H01M
4/621 20130101; H01M 4/134 20130101; Y02E 60/10 20130101; H01M
4/1395 20130101 |
Class at
Publication: |
429/218.1 ;
429/231.95; 429/217; 420/589 |
International
Class: |
H01M 4/58 20060101
H01M004/58; H01M 4/62 20060101 H01M004/62; C22C 30/04 20060101
C22C030/04 |
Claims
1. A lithium ion battery comprising a cathode, an anode, and an
electrolyte in electrical communication with both the anode and the
cathode, wherein the anode comprises an alloy composition
comprising a) silicon in an amount of 35 to 70 mole percent; b)
aluminum in an amount of 1 to 45 mole percent; c) a transition
metal in an amount of 5 to 25 mole percent; d) tin in an amount of
1 to 15 mole percent; e) indium in an amount up to 15 mole percent;
and e) a sixth element comprising yttrium, a lanthanide element, an
actinide element, or a combination thereof in an amount of 2 to 15
mole percent, wherein each mole percent is based on a total number
of moles of all elements except lithium in the alloy composition;
and the alloy composition is a mixture of an amorphous phase
comprising silicon and a nanocrystalline phase comprising (1) tin,
(2) indium, and (3) the sixth element.
2. The lithium ion battery of claim 1, wherein the amorphous phase
further comprises aluminum and the transition metal.
3. The lithium ion battery of claim 1, wherein the sixth element
comprises cerium, lanthanum, praseodymium, neodymium, or a
combination thereof.
4. The lithium ion battery of claim 1, wherein the nanocrystalline
phase is substantially free of silicon.
5. The lithium ion battery of claim 1, wherein the nanocrystalline
phase is substantially free of elemental tin, elemental indium, a
binary tin-indium compound, or a combination thereof.
6. The lithium ion battery of claim 1, wherein the alloy
composition further comprises less than 1 mole percent alkaline
earth metal.
7. The lithium ion battery of claim 1, wherein the alloy
composition further comprises an alkaline metal.
8. The lithium ion battery of claim 1, wherein the alloy
composition comprises particles having a maximum average dimension
of 1 to 60 micrometers.
9. The lithium ion battery of claim 1, wherein the alloy
composition has a single amorphous phase and a single
nanocrystalline phase.
10. The lithium ion battery of claim 1, wherein the alloy
composition is of Formula I
Si.sub.aAl.sub.bT.sub.cSn.sub.dIn.sub.eM.sub.fLi.sub.g (I) wherein
a is a in the range of 35 to 70; b is a number in the range of 1 to
45; T is a transition metal; c is a number in the range of 5 to 25;
d is a number in the range of 1 to 15; e is a number up to 15; M is
yttrium, a lanthanide element, an actinide element, or a
combination thereof; f is a number in the range of 2 to 15; the sum
of a+b+c+d+e+f is equal to 100; and g is a number in the range of 0
to [4.4(a+d+e)+b].
11. The lithium ion battery of claim 10, wherein the variable a is
a number in the range of 40 to 65; b is a number in the range of 1
to 25; c is a number in the range of 5 to 25; d is a number in the
range of 1 to 15; e is a number up to 15; and f is a number in the
range of 2 to 15.
12. The lithium ion battery of claim 10, wherein the variable a is
a number in the range of 40 to 55; b is a number in the range of 25
to 45; c is a number in the range of 5 to 25; d is a number in the
range of 1 to 15; e is a number up to 15; and f is a number in the
range of 2 to 15.
13. The lithium ion battery of claim 10, wherein the variable a is
a number in the range of 55 to 65; b is a number in the range of 10
to 20; c is a number in the range of 5 to 25; d is a number in the
range of 1 to 15; e is a number up to 15; and f is a number in the
range of 2 to 15.
14. The lithium ion battery of claim 10, wherein the anode further
comprises an organic binder comprising a polyimide.
15. The lithium ion battery of claim 1, wherein the anode further
comprises lithium metal.
16. A battery pack comprising at least one lithium ion battery
according to claim 1.
17. A method of preparing a lithium ion battery, said method
comprising: providing an anode comprising an alloy composition
comprising a) silicon in an amount of 35 to 70 mole percent; b)
aluminum in an amount of 1 to 45 mole percent; c) a transition
metal in an amount of 5 to 25 mole percent; d) tin in an amount of
1 to 15 mole percent; e) indium in an amount up to 15 mole percent;
and f) yttrium, a lanthanide element, an actinide element, or a
combination thereof in an amount of 2 to 15 mole percent, wherein
each mole percent is based on a total number of moles of all
elements except lithium in the alloy composition and wherein the
alloy composition is a mixture of an amorphous phase comprising
silicon and a nanocrystalline phase comprising tin and the sixth
element; providing a cathode and an electrolyte, wherein the
electrolyte is in electrical communication with both the cathode
and the anode.
18. The method of claim 17, wherein providing the alloy composition
comprises melt spinning the silicon, aluminum, tin, the transition
metal element, and the sixth element.
19. The method of claim 17, wherein providing the alloy composition
comprises initially forming a totally amorphous precursor material
and then annealing the precursor material to prepare the mixture of
the amorphous phase and the nanocrystalline phase.
20. The method of claim 17, wherein providing the alloy comprises:
forming a precursor material that comprises (i) amorphous material;
(ii) the nanocrystalline phase comprising tin, indium, and the
sixth element; (iii) at least one additional crystalline phase that
contains elemental tin, elemental indium, binary tin-indium, or a
combination thereof; and annealing the precursor material to remove
the additional crystalline phase.
21. The method of claim 17, wherein the nanocrystalline phase is
substantially free of silicon.
22. An alloy composition comprising a) silicon in an amount of 35
to 70 mole percent; b) aluminum in an amount of 1 to 45 mole
percent; c) a transition metal in an amount of 5 to 25 mole
percent; f) tin in an amount of 1 to 15 mole percent; g) indium in
an amount up to 15 mole percent; and e) a sixth element comprising
yttrium, a lanthanide element, an actinide element, or a
combination thereof in an amount of 2 to 15 mole percent, wherein
each mole percent is based on a total number of moles of all
elements except lithium in the alloy composition; and the alloy
composition is a mixture of an amorphous phase comprising silicon
and a nanocrystalline phase comprising (1) tin, (2) indium, and (3)
the sixth element.
Description
RELATED APPLICATION
[0001] This application claims priority from U.S. Provisional
Application No. 60/702,244, which was filed on Jul. 25, 2005 and is
hereby incorporated by reference.
FIELD OF INVENTION
[0002] Alloy compositions for lithium ion batteries are
described.
BACKGROUND
[0003] Rechargeable lithium ion batteries are included in a variety
of electronic devices. Most commercially available lithium ion
batteries have anodes that contain materials such as graphite that
are capable of incorporating lithium through an intercalation
mechanism during charging. Such intercalation-type anodes generally
exhibit good cycle life and coulombic efficiency. However, the
amount of lithium that can be incorporated per unit mass of
intercalation-type material is relatively low.
[0004] A second class of anode material is known that incorporates
lithium through an alloying mechanism during charging. Although
these alloy-type materials can often incorporate higher amounts of
lithium per unit mass than intercalation-type materials, the
addition of lithium to the alloy is usually accompanied with a
large volume change. Some alloy-type anodes exhibit relatively poor
cycle life and coulombic efficiency. The poor performance of these
alloy-type anodes may result from the formation of a two-phase
region during lithiation and delithiation. The two-phase region can
create internal stress within the alloy if one phase undergoes a
larger volume change than the other phase. This internal stress can
lead to the disintegration of the anode material over time.
[0005] Further, the large volume change accompanying the
incorporation of lithium can result in the deterioration of
electrical contact between the alloy, conductive diluent (e.g.,
carbon) particles, and binder that typically form the anode. The
deterioration of electrical contact, in turn, can result in
diminished capacity over the cycle life of the anode.
SUMMARY
[0006] Alloy compositions, lithium ion batteries, and methods of
making lithium ion batteries are provided. More specifically, the
lithium ion batteries have anodes that contain an alloy composition
that is a mixture of an amorphous phase and a nanocrystalline
phase.
[0007] In one aspect, a lithium ion battery is described that
contains a cathode, an anode, and an electrolyte that is in
electrical communication with both the anode and the cathode. The
anode includes an alloy composition that contains (a) silicon in an
amount of 35 to 70 mole percent, (b) aluminum in an amount of 1 to
45 mole percent, (c) a transition metal in an amount of 5 to 25
mole percent, (d) tin in an amount of 1 to 15 mole percent, (e)
indium in an amount up to 15 mole percent, and (f) a sixth element
that includes yttrium, a lanthanide element, an actinide element,
or a combination thereof in an amount of 2 to 15 mole percent. Each
mole percent is based on a total number of moles of all elements
except lithium in the alloy composition. The alloy composition is a
mixture of an amorphous phase that includes silicon and a
nanocrystalline phase that includes tin, indium, and the sixth
element.
[0008] In another aspect, a method of making a lithium ion battery
is described that includes preparing an anode that contains an
alloy composition, providing a cathode, and providing an
electrolyte that is in electrical communication with both the anode
and the cathode. The alloy composition contains (a) silicon in an
amount of 35 to 70 mole percent, (b) aluminum in an amount of 1 to
45 mole percent, (c) a transition metal in an amount of 5 to 25
mole percent, (d) tin in an amount of 1 to 15 mole percent, (e)
indium in an amount up to 15 mole percent, and (f) a sixth element
that includes yttrium, a lanthanide element, an actinide element,
or a combination thereof in an amount of 2 to 15 mole percent. Each
mole percent is based on a total number of moles of all elements
except lithium in the alloy composition. The alloy composition is a
mixture of an amorphous phase that includes silicon and a
nanocrystalline phase that includes tin, indium, and the sixth
element.
[0009] In yet another aspect, an alloy composition is described.
The alloy composition contains (a) silicon in an amount of 35 to 70
mole percent, (b) aluminum in an amount of 1 to 45 mole percent,
(c) a transition metal in an amount of 5 to 25 mole percent, (d)
tin in an amount of 1 to 15 mole percent, (e) indium in an amount
up to 15 mole percent, and (f) a sixth element that includes
yttrium, a lanthanide element, an actinide element, or a
combination thereof in an amount of 2 to 15 mole percent. Each mole
percent is based on a total number of moles of all elements except
lithium in the alloy composition. The alloy composition is a
mixture of an amorphous phase that includes silicon and a
nanocrystalline phase that includes tin, indium, and the sixth
element.
[0010] As used herein, the terms "a", "an", and "the" are used
interchangeably with "at least one" to mean one or more of the
elements being described.
[0011] The term "amorphous" refers to a material that lacks the
long-range atomic order characteristic of crystalline material, as
determined using x-ray diffraction techniques.
[0012] The terms "crystalline", "crystallite", and "crystals" refer
to materials that have long-range order as determined using x-ray
diffraction techniques. The crystalline materials have a maximum
dimension of at least about 5 nanometers. The terms
"nanocrystalline", "nanocrystallite", and "nanocrystals" refer to a
subset of crystalline materials that have a maximum dimension of
about 5 to about 50 nanometers. Some crystalline materials are
larger than nanocrystalline materials (i.e., some have a maximum
dimension larger than about 50 nanometers).
[0013] The term "electrochemically active" refers to a material
that reacts with lithium under conditions typically encountered
during charging of a lithium ion battery. The electrochemically
active material is usually in the form of a metal or alloy.
[0014] The term "electrochemically inactive" refers to a material
that does not react with lithium under conditions typically
encountered during charging of a lithium ion battery.
[0015] The electrochemically inactive material is usually in the
form of a metal or alloy.
[0016] The term "metal" refers to both metals and metalloids such
as silicon and germanium. The metal is often in an elemental state.
An "intermetallic" compound is a compound containing at least two
metals.
[0017] The term "lithiation" refers to the process of adding
lithium to the alloy composition (i.e., lithium ions are
reduced).
[0018] The term "delithiation" refers to the process of removing
lithium from the alloy composition (i.e., lithium atoms are
oxidized).
[0019] The term "charging" refers to a process of providing
electrical energy to a battery.
[0020] The term "discharging" refers to a process of removing
electrical energy from a battery (i.e., discharging is a process of
using the battery to do useful work).
[0021] The term "capacity" refers to the amount of lithium that can
be incorporated into the anode material (e.g., the alloy
composition) and has units of milliamp-hours (mAh). The term
"specific capacity" refers to the capacity per unit mass of the
anode material and has units of milliamp-hour/gram (mAh/g).
[0022] The term "cathode" refers to the electrode where
electrochemical reduction occurs during the discharging process.
During discharging, the cathode undergoes lithiation. During
charging, lithium atoms are removed from this electrode.
[0023] The term "anode" refers to the electrode where
electrochemical oxidation occurs during the discharging process.
During discharging, the anode undergoes delithiation. During
charging, lithium atoms are added to this electrode.
[0024] As used herein, a "number in the range of" includes the
endpoints of the range and all the numbers between the endpoints.
For example, a number in the range of 1 to 10 includes 1, 10, and
all the numbers between 1 and 10.
[0025] The above summary is not intended to describe each disclosed
embodiment or every implementation of the present invention. The
detailed description section that follows more particularly
exemplifies these embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] The invention can be more completely understood in
consideration of the following detailed description of various
embodiments of the invention in connection with the accompanying
drawings, in which:
[0027] FIG. 1 is the x-ray diffraction pattern of the alloy
composition Si.sub.60Al.sub.14Fe.sub.8TiInSn.sub.6(MM).sub.10 where
MM refers to mischmetal.
[0028] FIG. 2 is a plot of voltage versus capacity of an
electrochemical cell having an electrode that contains an alloy
composition Si.sub.60Al.sub.14Fe.sub.8TiInSn.sub.6(MM).sub.10.
[0029] FIG. 3 is the x-ray diffraction pattern of the alloy
composition
Si.sub.60Al.sub.14Fe.sub.8TiIn.sub.3Sn.sub.4(MM).sub.10.
[0030] FIG. 4 is a plot of voltage versus capacity of an
electrochemical cell having an electrode that contains an alloy
composition
Si.sub.60Al.sub.14Fe.sub.8TiIn.sub.3Sn.sub.4(MM).sub.10.
[0031] FIG. 5 is the x-ray diffraction pattern of the alloy
composition Si.sub.59Al.sub.16Fe.sub.8InSn.sub.6(MM).sub.10.
[0032] FIG. 6 is a plot of voltage versus capacity of an
electrochemical cell having an electrode that contains an alloy
composition Si.sub.59Al.sub.16Fe.sub.8InSn.sub.6(MM).sub.10.
[0033] FIG. 7 is a plot of voltage versus capacity of an
electrochemical cell having an electrode that contain lithium
powder and an alloy composition
Si.sub.60Al.sub.14Fe.sub.8TiInSn.sub.6(MM).sub.10.
[0034] While the invention is amenable to various modifications and
alternative forms, specifics thereof have been shown by way of
example in the drawings and will be described in detail. It should
be understood, however, that the intention is not to limit the
invention to the particular embodiments described. On the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the
invention.
DETAILED DESCRIPTION
[0035] Alloy compositions are described that can be included in the
anode of a lithium ion battery. The alloy compositions are a
mixture of an amorphous phase and a nanocrystalline phase. Compared
to materials that contain large crystallites (i.e., crystals having
a maximum dimension greater than about 50 nanometers), this mixture
can advantageously decrease the risk of anode disintegration over
time due to internal stress within the alloy composition.
Additionally, compared to materials that are entirely amorphous,
this mixture can advantageously result in anodes having an
increased rate of lithiation. Anodes having an increased rate of
lithiation can be recharged at a faster rate.
[0036] In one aspect, lithium ion batteries are provided that
include a cathode, an anode, and an electrolyte that is in
electrical communication with both the cathode and the anode. The
alloy composition contains (a) silicon, (b) aluminum, (c) a
transition metal, (d) tin, (e) indium, and (f) a sixth element that
includes yttrium, a lanthanide element, an actinide element, or a
combination thereof. The amorphous phase contains silicon while the
nanocrystalline phase is substantially free of silicon. The
nanocrystalline phase contains an intermetallic compound that
includes (1) tin, (2) indium, and (3) the sixth element.
[0037] The amorphous nature of the alloy compositions can be
characterized by the absence of sharp peaks in the x-ray
diffraction pattern. The x-ray diffraction pattern can have broad
peaks, such as peaks having a peak width at half the maximum peak
height corresponding to at least 5 degrees two theta, at least 10
degrees two theta, or at least 15 degrees two theta using a copper
target (i.e., copper K.alpha.1 line, copper K.alpha.2 line, or a
combination thereof).
[0038] Nanocrystalline materials typically have a maximum dimension
of about 5 nanometers to about 50 nanometers. The crystalline size
can be determined from the width of an x-ray diffraction peak using
the Sherrer equation. Narrower x-ray diffraction peaks correspond
to larger crystal sizes. The x-ray diffraction peaks for
nanocrystalline materials typically have a peak width at half the
maximum peak height corresponding to less than 5 degrees two theta,
less than 4 degrees two theta, less than 3 degrees two theta, less
than 2 degrees two theta, or less than 1 degree two theta using a
copper target (i.e., copper K.alpha.1 line, copper K.alpha.2 line,
or a combination thereof). The nanocrystalline material has a peak
width at half of the maximum peak height corresponding to at least
0.2 degrees two theta, at least 0.5 degrees two theta, or at least
1 degree two theta using a copper target.
[0039] Because the rate of lithiation is generally greater for
nanocrystalline material than for amorphous material, it is
desirable to include some nanocrystalline material in the alloy
composition. The presence of elemental silicon in a crystalline
phase, however, can result in the formation of crystalline
Li.sub.15Si.sub.4 during cycling when the voltage drops below about
50 mV versus a metallic Li/Li ion reference electrode. The
formation of crystalline Li.sub.15Si.sub.4 during lithiation can
adversely affect the cycle life of the anode (i.e., the capacity
tends to diminish with each cycle of lithiation and delithiation).
To minimize or prevent the formation of Li.sub.15Si.sub.4 crystals,
it is advantageous for silicon to be present in the amorphous phase
and to remain in the amorphous phase after repetitive cycles of
lithiation and delithiation. The addition of a transition metal
facilitates the formation of an amorphous silicon-containing phase
and minimizes or prevents the formation of a crystalline
silicon-containing phase (e.g., crystalline elemental silicon or
crystalline silicon-containing compounds).
[0040] The nanocrystalline phase of the alloy composition includes
tin, which is another electroactive material, rather than silicon.
The presence of crystalline elemental tin, however, can be
detrimental to the capacity when the anode is subjected to
repetitive cycles of lithiation and delithiation. As used herein,
the term "elemental" refers to an element of the periodic table
(e.g., tin, silicon, indium, or the like) that is present in an
elemental form (i.e., as a pure element) rather than combined with
another element in the form of a compound such as an intermetallic
compound.
[0041] To minimize the formation of crystalline elemental tin, an
intermetallic compound is formed that contains (1) tin, (2) indium,
and (3) a sixth element that contains yttrium, a lanthanide
element, an actinide element, or a combination thereof are added to
the alloy composition. The intermetallic compound can be, for
example, of formula [Sn.sub.(1-x)In.sub.x].sub.3M where M is an
element that contains yttrium, a lanthanide element, an actinide
element, or a combination thereof and x is a positive number less
than 1. In the absence of the indium and the sixth element, it can
be difficult to control the crystalline size using some formation
processes. For example, when an alloy is formed using a melt
spinning technique without any of the sixth element or indium,
relatively large crystals of elemental tin can form.
[0042] Indium tends to impede the formation of crystalline
elemental tin and increases the capacity of the alloy composition.
Additionally, the addition of indium tend to facilitate the use of
melt processing techniques such as melt spinning to form the alloy
composition and increases the likelihood that an amorphous phase
will form rather than a large crystalline phase.
[0043] The alloy composition includes an amorphous phase that
includes all of the silicon. The amorphous phase typically includes
all or a portion of the aluminum and all or a portion of the
transition metal. The alloy further includes a nanocrystalline
phase that includes an intermetallic compound containing tin,
indium, and the sixth element. The nanocrystalline phase can
include all or a portion of the tin, all or a portion of the
indium, and all or a portion of the sixth element. The
nanocrystalline phase is substantially free of elemental tin,
elemental silicon, elemental indium, and an indium-tin binary
intermetallic compound. As used herein, the term "substantially
free" when referring to the nanocrystalline phase means that the
substance (e.g., elemental silicon, elemental tin, elemental
indium, or the indium-tin binary intermetallic compound) cannot be
detected using x-ray diffraction techniques.
[0044] The specific capacity (i.e., the capacity per gram) of the
alloy compositions is usually at least 200 mAh/g. In some
embodiment, the specific capacity can be at least 400 mAh/g, at
least 600 mAh/g, at least 800 mAh/g, at least 1000 mAh/g, at least
1200 mAh/g, at least, at least 1600 mAh/g, or at least 2000 mAh/g.
The specific capacity is typically measured during the discharging
portion of the second cycle of lithiation and delithiation.
[0045] As used herein, the term "mole percent" when referring to
constituents of the alloy composition is calculated based on a
total number of moles of all elements in the alloy composition
except lithium. For example, the mole percent silicon in an alloy
that contains silicon, aluminum, transition metal, tin, indium, and
a sixth element is calculated by multiplying the moles of silicon
by 100 and dividing this product by the total moles of all elements
except lithium in the alloy composition (e.g., moles of
silicon+moles of aluminum+moles of transition metal+moles of
tin+mole of indium+moles of sixth element).
[0046] All of the silicon is generally in the amorphous phase.
Silicon is present in the alloy composition in an amount of 35 to
70 mole percent based on the total number of moles of all elements
except lithium in the alloy composition. If the amount of silicon
is too low, the capacity can be unacceptably low. If the amount of
silicon is too high, however, silicon-containing crystals tend to
form. The presence of crystalline silicon, at least in some
embodiments, can lead to the formation of Li.sub.15Si.sub.4 during
cycling when the voltage drops below about 50 mV versus a metallic
Li/Li ion reference electrode. Crystalline Li.sub.15Si.sub.4 can
detrimentally affect the cycle life of a lithium ion battery.
[0047] The alloy composition contains at least 35 mole percent, at
least 45 mole percent, at least 50 mole percent, at least 55 mole
percent, or at least 60 mole percent silicon. The alloy composition
can contain up to 70 mole percent, up to 65 mole percent, or up to
60 mole percent silicon. For example, the alloy composition can
contain 40 to 70 mole percent, 50 to 70 mole percent, 55 to 70 mole
percent, or 55 to 65 mole percent silicon.
[0048] Aluminum is another element that is present in the alloy
composition. The aluminum is typically present in the amorphous
phase and, along with the transition metal, facilitates the
formation of the amorphous phase that contains all of the silicon.
The aluminum can be electrochemically active, electrochemically
inactive, or a combination thereof. If the aluminum is present as
elemental aluminum, it is often electrochemically active.
Electrochemically active aluminum can enhance the capacity of the
alloy composition. If the aluminum is present as an intermetallic
compound with a transition metal, however, it can be
electrochemically inactive. As an electrochemically inactive
material, an aluminum intermetallic compound can function as a
matrix for the electrochemically active components.
[0049] Aluminum is present in the alloy composition in an amount of
1 to 45 mole percent based on the total number of moles of all
elements except lithium in the alloy composition. The addition of
aluminum to the alloy composition often lowers the melting point,
which can facilitate the use of various melt processing technique
such as melt spinning to form the alloy composition. Melt
processing techniques are often less expensive than techniques such
as sputtering. If the aluminum level is too low, it can be more
difficult to form an amorphous phase that contains all of the
silicon. Too much aluminum, however, can detrimentally affect the
cycle life of the lithium ion battery. That is, too much aluminum
can result in an unacceptably large capacity decrease when the
anode is subjected to repetitive cycles of lithiation and
delithiation.
[0050] The alloy composition contains up to 45 mole percent, up to
40 mole percent, up to 35 mole percent, up to 30 mole percent, up
to 25 mole percent, up to 20 mole percent, or up to 15 mole percent
aluminum. The aluminum in the alloy composition is often present in
an amount of at least 1 mole percent, at least 2 mole percent, at
least 5 mole percent, or at least 10 mole percent. For example, the
alloy composition can contain 2 to 40 mole percent, 3 to 40 mole
percent, 5 to 40 mole percent, 10 to 40 mole percent, 10 to 30 mole
percent, or 10 to 20 mole percent aluminum.
[0051] The alloy composition also includes a transition metal in an
amount of 5 to 25 mole percent based on the total number of moles
of all elements except lithium in the alloy composition. Suitable
transition metals include, but are not limited to, titanium,
vanadium, chromium, manganese, iron, cobalt, nickel, copper,
zirconium, niobium, molybdenum, tungsten, and combinations thereof.
The transition metal, in combination with aluminum, facilitates the
formation of the amorphous phase. If too little transition metal is
included in the alloy composition, it can be more difficult to form
an amorphous phase that includes all of the silicon. If the
transition metal concentration is too high, however, the capacity
of the alloy composition can be unacceptably low because the
transition metal is electrochemically inactive or combines with
other components such as aluminum to form an intermetallic compound
that is electrochemically inactive.
[0052] The transition element is present in an amount of at least 5
mole percent, at least 8 mole percent, at least 10 mole percent, or
at least 12 mole percent. The alloy composition contains up to 25
mole percent, up to 20 mole percent, or up to 15 mole percent
transition metal. For example, the alloy composition includes 5 to
20 mole percent, 5 to 15 mole percent, 8 to 25 mole percent, 8 to
20 mole percent, or 10 to 25 mole percent transition metal.
[0053] Tin is yet another element present in the alloy composition.
Tin is typically present in the nanocrystalline phase as an
intermetallic compound with (1) indium and (2) a sixth metal that
contains yttrium, a lanthanide element, an actinide element, or a
combination thereof. The nanocrystalline material is often of
formula [Sn.sub.(1-x)In.sub.x].sub.3M where M is an element that
contains yttrium, a lanthanide element, an actinide element, or a
combination thereof and x is a positive number less than 1.
Depending on the relative ratios of tin, indium, and the sixth
element, multiple nanocrystalline materials can be present in the
alloy composition. For example, the nanocrystalline material can
include Sn.sub.3M, In.sub.3M, or both in addition to
[Sn.sub.(1-x)InX].sub.3M.
[0054] The nanocrystalline phase can increase the rate of
lithiation of the alloy composition, particularly during the first
cycle of lithiation and delithiation. Although not wanting to be
bound by theory, the nanocrystalline phase may be analogous to
veins through the amorphous phase. The nanocrystalline phase may
provide a conduction path for lithium throughout the alloy
composition, which may allow lithium to diffuse quickly along the
grain boundaries between the nanocrystalline phase and the
amorphous phase.
[0055] The alloy composition contains 1 to 15 mole percent tin
based on the total number of moles of all elements except lithium
in the alloy composition. If too much tin is present, crystalline
tin can form rather than a nanocrystalline tin-containing,
intermetallic compound. Crystalline elemental tin detrimentally
affects the capacity when the anode is subjected to repetitive
cycles of lithiation and delithiation. That is, too much tin can
cause the capacity to decrease unacceptably when the anode is
subjected to repetitive cycles of lithiation and delithiation. If
the amount of tin is too low, however, the rate of lithiation may
be comparable to that of an amorphous material.
[0056] Tin is present in an amount up to 15 mole percent, up to 12
mole percent, up to 10 mole percent, up to 9 mole percent, up to 8
mole percent, up to 7 mole percent, up to 6 mole percent, or up to
5 mole percent. Tin is usually present in an amount of at least I
mole percent, at least 2 mole percent, at least 3 mole percent, at
least 4 mole percent, or at least 5 mole percent. For example, the
alloy composition can contain 1 to 12 mole percent, 1 to 10 mole
percent, 1 to 9 mole percent, 2 to 9 mole percent, 2 to 8 mole
percent, or 3 to 9 mole percent tin.
[0057] Indium is present in the alloy composition in an amount up
to 15 mole percent based on the total number of all elements except
lithium in the alloy composition. Indium is part of the
nanocrystalline phase in the form of an intermetallic compound that
also includes tin and the sixth element. The alloy composition is
typically substantially free of crystalline elemental indium. The
alloy composition is typically substantially free of crystalline
binary indium-tin intermetallic compounds such as
Sn.sub.(1-y)In.sub.y where y is a number less than 1 such as, for
example, Sn.sub.0.8In.sub.0.2.
[0058] The presence of indium in the nanocrystalline intermetallic
compound typically improves cycle life of the alloy composition.
More specifically, indium improves the retention of the capacity
after repeated cycles of lithiation and delithiation. If too much
indium is present, crystalline elemental indium can form rather
than a nanocrystalline intermetallic compound with tin and the
sixth element. Crystalline elemental indium can disadvantageously
lead to a decreased capacity when the anode is subjected to
repetitive cycles of lithiation and delithiation.
[0059] The alloy composition often contains at least 0.1 mole
percent, at least 0.2 mole percent, at least 0.5 mole percent, or
at least 1 mole percent indium. The amount of indium in the alloy
composition is often up to 15 mole percent, up to 12 mole percent,
up to 10 mole percent, up to 8 mole percent, or up to 6 mole
percent. For example, the alloy composition can contain 0.1 to 15
mole percent, 0.1 to 10 mole percent, 0.2 to 10 mole percent, 0.5
to 10 mole percent, 1 to 10 mole percent, or 2 to 10 mole percent
indium.
[0060] A sixth element is included in the alloy composition that
contains yttrium, a lanthanide element, an actinide element, or a
combination thereof in an amount of 2 to 15 mole percent based on
the total number of moles all elements except lithium in the alloy
composition. The sixth element is included in the nanocrystalline
phase and combines with tin and indium to form an intermetallic
compound. If the alloy composition contains too much of the sixth
element, the capacity can be reduced because the sixth element is
typically electrochemically inactive. On the other hand, if the
amount of the sixth element is too low, there can be some tin that
is in the form of crystalline elemental tin rather than in the form
of an intermetallic compound. The presence of crystalline elemental
tin can deleteriously affect the capacity when the lithium ion
battery is subjected to repetitive cycles of lithiation and
delithiation. The nanocrystalline phase is substantially free of a
stoichiometric compound such as a silicide formed by combining
silicon with the sixth element. A stoichiometric compound has a
defined ratio between the elements in the compound with the ratio
being a rational number.
[0061] Suitable lanthanide elements include lanthanum, cerium,
praseodymium, neodymium, promethium, samarium, europium,
gadolinium, terbium, dysprosium, holmium, erbium, thulium,
ytterbium, and lutetium. Suitable actinide elements include
thorium, actinium, and protactinium. Some alloy compositions
contain a lanthanide elements selected, for example, from cerium,
lanthanum, praseodymium, neodymium, or a combination thereof.
[0062] The sixth element can be a mischmetal, which is an alloy of
various lanthanides. Some mischmetals contains, for example, 45 to
60 weight percent cerium, 20 to 45 weight percent lanthanum, 1 to
10 weight percent praseodymium, and 1 to 25 weight percent
neodymium. Other mischmetals contains 30 to 40 weight percent
lanthanum, 60 to 70 weight percent cerium, less than 1 weight
percent praseodymium, and less than 1 weight percent neodymium.
Still other mischmetal contains 40 to 60 weight percent cerium and
40 to 60 weight percent lanthanum. The mischmetals often includes
small impurities (e.g., less than 1 weight percent, less than 0.5
weight percent, or less than 0.1 weight percent) such as, for
example, iron, magnesium, silicon, molybdenum, zinc, calcium,
copper, chromium, lead, titanium, manganese, carbon, sulfur, and
phosphorous. The mischmetal often has a lanthanide content of at
least 97 weight percent, at least 98 weight percent, or at least 99
weight percent. One exemplary mischmetal that is commercially
available from Alfa Aesar, Ward Hill, Mass. with 99.9 weight
percent purity contains approximately 50 weight percent cerium, 18
weight percent neodymium, 6 weight percent praseodymium, 22 weight
percent lanthanum, and 3 weight percent other rare earths.
[0063] The alloy composition contains at least 2 mole percent, at
least 3 mole percent, or at least 5 mole percent of the sixth
element. The sixth element can be present in amounts up to 15 mole
percent, up to 12 mole percent, or up to 10 mole percent in the
alloy composition. For example, the alloy composition can contain 3
to 15 mole percent, 5 to 15 mole percent, 3 to 12 mole percent, or
3 to 10 mole percent of the sixth element. In some embodiments, the
sixth element is a lanthanide element or a mixture of lanthanide
elements.
[0064] The alloy composition is substantially free of an alkaline
earth metal such as calcium, barium, magnesium, and the like. As
used herein, the term "substantially free" with reference to an
alkaline earth metal means that the alloy composition contains no
more than 1 mole percent alkaline earth, no more than 0.5 mole
percent alkaline earth, no more than 0.2 mole percent alkaline
earth, or no more than 0.1 mole percent alkaline earth. An alkaline
earth, if present in the alloy composition, is typically present as
an impurity of another component and is not purposefully added.
[0065] The alloy composition can further include an alkali metal
such as lithium. Prior to the first lithiation reaction, the alloy
composition typically contains little or no lithium. After the
first lithiation, the amount of lithium can vary but is typically
greater than zero even after the lithium ion battery has been
discharged. That is, the anode containing the alloy composition
often has at least a small amount of irreversible capacity.
[0066] The alloy compositions are often of Formula I:
Si.sub.aAl.sub.bT.sub.cSn.sub.dIn.sub.eM.sub.fLi.sub.g (I) where a
is a number in the range of 35 to 70; b is a number in the range of
1 to 45; T is a transition metal; c is a number in the range of 5
to 25; d is a number in the range of 1 to 15; e is a number up to
15; M is yttrium, a lanthanide element, or a combination thereof; f
is a number in the range of in the range of 2 to 15; and the sum of
a+b+c+d+e+f is equal to 100. The variable g is a number in the
range of 0 to [4.4(a+d+e)+b].
[0067] In some exemplary compositions according to Formula I, the
variable a is a number in the range of 40 to 65; b is a number in
the range of 1 to 25; c is a number in the range of 5 to 25; d is a
number in the range of 1 to 15; e is a number up to 15; and f is a
number in the range of 2 to 15. In other exemplary compositions
according to Formula I, the variable a is a number in the range of
40 to 55; b is a number in the range of 25 to 45; c is a number in
the range of in the range of 5 to 25; d is a number in the range of
1 to 15; e is a number up to 15; and f is a number in the range of
2 to 15. In still other exemplary compositions, the variable a is a
number in the range of 55 to 65; b is a number in the range of 10
to 20; c is a number in the range of 5 to 25; d is a number in the
range of 1 to 15; e is a number up to 15; and f is a number in the
range of 2 to 15.
[0068] The alloy composition of the anode can be in the form of a
thin film or powder, the form depending on the technique chosen to
prepare the materials. Suitable methods of preparing the alloy
compositions include, but are not limited to, sputtering, chemical
vapor deposition, vacuum evaporation, melt processing such as melt
spinning, splat cooling, spray atomization, electrochemical
deposition, and ball milling.
[0069] The method of making the alloy composition often involves
forming an amorphous precursor material and then annealing the
precursor material at a temperature in the range of about
150.degree. C. to about 400.degree. C. Annealing tends to convert
the precursor material that is entirely amorphous into an alloy
composition that is a mixture of an amorphous phase and a
nanocrystalline phase. The annealing step is typically conducted by
heating the precursor material in an inert environment such as
argon or helium.
[0070] Sputtering is a procedure for producing amorphous precursor.
The different elements can be sputtered simultaneously or
sequentially. For example, the elements can be sequentially
sputter-coated on a substrate such as a copper substrate. The
substrates can be positioned near the edge of a turntable (e.g., 25
inch diameter) that rotates continuously below multiple sputtering
sources that are operating continuously. A layer of one material
can be deposited as the substrate passes under the first sputtering
source, and additional layers of different material can be
deposited as the substrate passes under the other sputtering
sources. The amount of material deposited from each sputtering
source can be controlled by varying the rotation speed of the
turntable and by varying the sputtering rates. Suitable sputtering
methods are further described in U.S. Pat. No. 6,203,944 B1 (Turner
et al.); U.S. Pat. No. 6,436,578 B1 (Turner et al.); and U.S. Pat.
No. 6,699,336 B2 (Turner et al.), all of which are incorporated
herein by reference.
[0071] Melt processing is another procedure that can be used to
produce precursors or for producing alloy compositions that are a
mixture of amorphous materials and nanocrystalline materials. Such
processes are described generally, for example, in Amorphous
Metallic Alloys, F. E. Luborsky, ed., Chapter 2, Butterworth &
Co., Ltd., 1983. Ingots containing the reactants can be melted in a
radio frequency field and then ejected through a nozzle onto a
surface of a rotating wheel (e.g., a copper alloy wheel) that can
be cooled. Because the surface temperature of the rotating wheel is
substantially lower than the temperature of the melt, contact with
the surface of the rotating wheel quenches the melt. Rapid
quenching minimizes the formation of crystalline material and
favors the formation of amorphous materials. Suitable melt
processing methods are further described in U.S. Pat. No. 6,699,336
B2 (Turner et al.), incorporated herein by reference. The
melt-processed material can be in the form, for example, of a
ribbon or a thin film.
[0072] In some melt processing procedures, depending on the
quenching rate and the particular material, the resulting material
can be a mixture of an amorphous phase and a single nanocrystalline
phase that includes an intermetallic compound of tin, indium, and
the sixth element. In other melt processing procedures, however,
the melt-processed material is a precursor that contains (1) an
amorphous phase, (2) a ternary nanocrystalline phase that includes
an intermetallic compound of tin, indium and the sixth element, and
(3) a crystalline (e.g., nanocrystalline) elemental tin phase, a
crystalline indium phase, a crystalline binary tin-indium phase of
formula Sn.sub.(1-y)In.sub.y where y is a positive number less than
1 such as, for example, Sn.sub.0.8In.sub.0.2, or a combination
thereof. The crystalline elemental tin phase, crystalline indium
phase, and the crystalline binary tin-indium phase can often be
removed by annealing the melt-processed precursor material at a
temperature in the range of about 150.degree. C. to about
400.degree. C. under an inert atmosphere. In still other melt
processing methods, the melt-processed material is a precursor that
contains only amorphous materials. The precursor can be annealed at
a temperature in the range of about 150.degree. C. to about
400.degree. C. under an inert atmosphere to prepare the alloy
composition that contains both an amorphous phase and a
nanocrystalline phase.
[0073] The sputtered or melt processed alloy compositions can be
further treated to produce powdered materials. For example, a
ribbon or thin film of the alloy composition can be pulverized to
form a powder. The powder can be formed before or after any
annealing step. Exemplary powders have a maximum dimension that is
no greater than 60 micrometers, no greater than 40 micrometers, or
no greater than 20 micrometers. The powders often have a maximum
dimension of at least 1 micrometer, at least 2 micrometers, at
least 5 micrometers, or at least 10 micrometers. For example,
suitable powders often have a maximum dimension of 1 to 60
micrometers, 10 to 60 micrometers, 20 to 60 micrometers, 40 to 60
micrometers, 1 to 40 micrometers, 2 to 40 micrometers, 10 to 40
micrometers, 5 to 20 micrometers, or 10 to 20 micrometers.
[0074] In some embodiments, the anode contains the alloy
composition dispersed in an elastomeric polymer binder. Exemplary
elastomeric polymer binders include polyolefins such as those
prepared from ethylene, propylene, or butylene monomers;
fluorinated polyolefins such as those prepared from vinylidene
fluoride monomers; perfluorinated polyolefins such as those
prepared from hexafluoropropylene monomer; perfluorinated
poly(alkyl vinyl ethers); perfluorinated poly(alkoxy vinyl ethers);
or combinations thereof. Specific examples of elastomeric polymer
binders include terpolymers of vinylidene fluoride,
tetrafluoroethylene, and propylene; and copolymers of vinylidene
fluoride and hexafluoropropylene. Commercially available
fluorinated elastomers include those sold by Dyneon, LLC, Oakdale,
Minn. under the trade designation "FC-2178", "FC-2179", and
"BRE-7131X".
[0075] In some anodes, the elastomeric binders are crosslinked.
Crosslinking can improve the mechanical properties of the polymer
and can improve the contact between the alloy composition and any
electrically conductive diluent that may be present.
[0076] In other anodes, the binder is a polyimide such as the
aliphatic or cycloaliphatic polyimides described in U.S. patent
application Ser. No. 11/218,448 filed on Sep. 1, 2005. Such
polyimide binders have repeating units of Formula II ##STR1## where
R.sup.1 is aliphatic or cycloaliphatic; and R.sup.2 is aromatic,
aliphatic, or cycloaliphatic.
[0077] The aliphatic or cycloaliphatic polyimide binders may be
formed, for example, using a condensation reaction between an
aliphatic or cycloaliphatic polyanhydride (e.g., a dianhydride) and
an aromatic, aliphatic or cycloaliphatic polyamine (e.g., a diamine
or triamine) to form a polyamic acid, followed by chemical or
thermal cyclization to form the polyimide. The polyimide binders
may also be formed using reaction mixtures additionally containing
aromatic polyanhydrides (e.g., aromatic dianhydrides), or from
reaction mixtures containing copolymers derived from aromatic
polyanhydrides (e.g., aromatic dianhydrides) and aliphatic or
cycloaliphatic polyanhydrides (e.g., aliphatic or cycloaliphatic
dianhydrides). For example, about 10 to about 90 percent of the
imide groups in the polyimide may be bonded to aliphatic or
cycloaliphatic moieties and about 90 to about 10 percent of the
imide groups may be bonded to aromatic moieties. Representative
aromatic polyanhydrides are described, for example, in U.S. Pat.
No. 5,504,128 (Mizutani et al.).
[0078] An electrically conductive diluent can be mixed with the
alloy composition in the anode. Exemplary electrically conductive
diluents include, but are not limited to, carbon, metal, metal
nitrides, metal carbides, metal silicides, and metal borides. In
some anodes, the electrically conductive diluents are carbon blacks
such as those commercially available from MMM Carbon of Belgium
under the trade designation "SUPER P" and "SUPER S" or from Chevron
Chemical Co. of Houston, Tex. under the trade designation
"SHAWINIGAN BLACK"; acetylene black; furnace black; lamp black;
graphite; carbon fibers; or combinations thereof.
[0079] The anode can further include an adhesion promoter that
promotes adhesion of the alloy composition and the electrically
conductive diluent to the elastomeric polymer binder. The
combination of an adhesion promoter and elastomeric polymer binder
accommodates, at least partially, volume changes that may occur in
the alloy composition during repeated cycles of lithiation and
delithiation. The adhesion promoter can be part of the binder
(e.g., in the form of a functional group) or can be in the form a
coating on the alloy composition, the electrically conductive
diluent, or a combination thereof. Examples of adhesion promoters
include, but are not limited to, silanes, titanates, and
phosphonates as described in U.S. Patent Application 2003/0058240,
the disclosure of which is incorporated herein by reference.
[0080] The anode can be partially lithiated prior to or during the
battery assembly process. Adding lithium to the anode can increase
the energy delivered by the battery during discharging. In some
embodiments, the anode is partially lithiated by dispersing a
lithium powder, the alloy composition, and a conductive diluent in
a solution of a polymer binder. The dispersion can be coated, dried
to remove any solvent, and cured to form the electrode. In other
embodiments, lithium foil or a lithium metal powder can be added to
the surface of a previously cured electrode. In the case of a
lithium metal powder, the powder can be distributed 1) by
sprinkling the powder directly onto the surface of the electrode or
2) by dispersing the lithium metal powder in a volatile solvent
that is non-reactive, followed by evenly coating the lithium
dispersion onto the electrode surface and evaporating off the
solvent. The lithium foil or lithium metal powder can then be
affixed to the electrode by a calendaring process. Although anodes
that contain lithium can be heated before battery assembly to react
the lithium with the other components of the anode, such anodes are
typically assembled into batteries without heating. During the
battery assembly process, the lithium can react with the other
components of the anode coating when electrolyte is added.
[0081] Any suitable electrolyte can be included in the lithium ion
battery. The electrolyte can be in the form of a solid or liquid.
Exemplary solid electrolytes include polymeric electrolytes such as
polyethylene oxide, polytetrafluoroethylene, polyvinylidene
fluoride, fluorine-containing copolymers, polyacrylonitrile, or
combinations thereof. Exemplary liquid electrolytes include
ethylene carbonate, fluoroethylene carbonate, dimethyl carbonate,
diethyl carbonate, propylene carbonate, gamma-butyrolactone,
tetrahydrofuran, 1,2-dimethoxyethane, dioxolane,
4-fluoro-1,3-dioxalan-2-one, or combinations thereof. The
electrolyte includes a lithium electrolyte salt such as LiPF.sub.6,
LiBF.sub.4, LiClO.sub.4, LiN(SO.sub.2CF.sub.3).sub.2,
LiN(SO.sub.2CF.sub.2CF.sub.3).sub.2, and the like.
[0082] The electrolyte can include a redox shuttle molecule, an
electrochemically reversible material that during charging can
become oxidized at the cathode, migrate to the anode where it can
become reduced to reform the unoxidized (or less-oxidized) shuttle
species, and migrate back to the cathode. Exemplary redox shuttle
molecules include those described in U.S. Pat. No. 5,709,968
(Shimizu), U.S. Pat. No. 5,763,119 (Adachi), U.S. Pat. No.
5,536,599 (Alamgir et al.), U.S. Pat. No. 5,858,573 (Abraham et
al.), U.S. Pat. No. 5,882,812 (Visco et al.), U.S. Pat. No.
6,004,698 (Richardson et al.), U.S. Pat. No. 6,045,952 (Kerr et
al.), and U.S. Pat. No. 6,387,571 B1 (Lain et al.); in PCT
Published Patent Application No. WO 01/29920 A1 (Richardson et al.)
; and in U.S. Patent Application Ser. No. 11/130850 filed on May
17, 2005 (Dahn et al.) and Ser. No. 11/130849 filed on May 17, 2005
(Dahn et al.); U.S. Provisional Patent Application No. 60/743,314
filed on Feb. 17, 2006 (Dahn et al.); and U.S. Patent Application
Publication No. 2005-0221196A1.
[0083] Any suitable cathode known for use in lithium ion batteries
can be utilized. Some exemplary cathodes include lithium transition
metal oxide such as lithium cobalt dioxide, lithium nickel dioxide,
and lithium manganese dioxide. Other exemplary cathodes are
disclosed in U.S. Pat. No. 6,680,145 B2 (Obrovac et al.),
incorporated herein by reference, and include transition metal
grains in combination with lithium-containing grains. Suitable
transition metal grains include, for example, iron, cobalt,
chromium, nickel, vanadium, manganese, copper, zinc, zirconium,
molybdenum, niobium, or combinations thereof with a grain size no
greater than about 50 nanometers. Suitable lithium-containing
grains can be selected from lithium oxides, lithium sulfides,
lithium halides (e.g., chlorides, bromides, iodides, or fluorides),
or combinations thereof. These particles can be used alone or in
combination with a lithium-transition metal oxide material such as
lithium cobalt dioxide.
[0084] In some lithium ion batteries with solid electrolytes, the
cathode can include LiV.sub.3O.sub.8 or LiV.sub.2O.sub.5. In other
lithium ion batteries with liquid electrolytes, the cathode can
include LiCoO.sub.2, LiCo.sub.0.2Ni.sub.0.8O.sub.2,
LiMn.sub.2O.sub.4, LiFePO.sub.4, or LiNiO.sub.2.
[0085] The lithium ion batteries can be used as a power supply in a
variety of applications. For example, the lithium ion batteries can
be used in power supplies for electronic devices such as computers
and various hand-held devices, motor vehicles, power tools,
photographic equipment, and telecommunication devices. Multiple
lithium ion batteries can be combined to provide a battery
pack.
EXAMPLES
[0086] Aluminum, silicon, iron, titanium, zirconium, tin, and
cobalt were obtained from Alfa Aesar, Ward Hill, Mass. or Aldrich,
Milwaukee, Wis. Indium was obtained from Indium Corporation of
America, Utica, N.Y. These materials had a purity of at least 99.8
weight percent. A mixture of rare earth elements, also known as
mischmetal (MM), was also obtained from Alfa Aesar with 99.0 weight
percent minimum rare earth content which contained approximately 50
weight percent cerium, 18 weight percent neodymium, 6 weight
percent praseodymium, 22 weight percent lanthanum, and 4 weight
percent other rare earth elements.
[0087] The alloy compositions were formed into electrodes and
characterized in electrochemical cells using a lithium metal
counter electrode.
Example 1
Si.sub.60Al.sub.14Fe.sub.8TiInSn.sub.6(MM).sub.10
[0088] An alloy composition
Si.sub.60Al.sub.14Fe.sub.8TiInSn.sub.6(MM).sub.10 was prepared by
mixing 17.606 g of silicon chips, 3.947 g of aluminum shot, 4.668 g
of iron lumps, 0.500 g titanium sponge, 7.441 g tin shot, 1.200 g
indium, and 14.639 g of mischmetal chunks. The mixture was melted
together on a carbon hearth in an argon filled arc furnace
purchased from Advanced Vacuum Systems, Ayer, Mass. The resulting
ingot had a composition of Si.sub.60Al.sub.14Fe.sub.8TiSn.sub.6InMm
and was broken into pieces having dimensions of about 1 cm in all
directions.
[0089] The ingots were then further processed by melt spinning in a
melt-spinning apparatus that included a vacuum chamber having a
cylindrical quartz glass crucible (16 mm internal diameter and 140
mm length) with a 0.35 mm orifice that was positioned above a
rotating cooling wheel. The rotating cooling wheel (10 mm thick and
203 mm diameter) was fabricated from a copper alloy (Ni--Si--Cr--Cu
C18000 alloy, 0.45 weight percent chromium, 2.4 weight percent
nickel, 0.6 weight percent silicon with the balance being copper)
that is commercially available from Nonferrous Products, Inc. from
Franklin, Ind. Prior to processing, the edge surface of the cooling
wheel was polished using a rubbing compound (commercially available
from 3M, St. Paul, Minn. under the trade designation IMPERIAL
MICROFINISHING) and then wiped with mineral oil to leave a thin
film.
[0090] After placing 15 g of the ingot in the crucible, the melt
spinning apparatus was evacuated to 80 mT (milliTorr) and then
filled with helium gas to 200 T. The ingot was melted using radio
frequency induction. As the temperature reached 1300.degree. C.,
400 T helium pressure was applied to the surface of the molten
material and a sample was extruded through a nozzle onto the
spinning (5031 revolutions per minute) cooling wheel. Ribbon strips
were formed that had a width of 1 mm and a thickness of 10
micrometers.
[0091] FIG. 1 shows the x-ray diffraction (XRD) pattern of the
resulting melt-spun ribbon sample taken with a Siemens D500 x-ray
diffractometer equipped with a copper target (K.alpha.1, K.alpha.2
lines). The XRD pattern shows that the alloy contained an amorphous
phase and a nanocrystalline phase. The broad hump is indicative of
amorphous material and the individual peaks are of a width
indicative of nanocrystalline material The XRD pattern lacks sharp
peaks associated with elemental silicon, elemental tin, elemental
indium, or a binary intermetallic compound of tin and indium.
[0092] The following components were added to a 40 ml tungsten
carbide milling vessel containing two 10 mm diameter and ten 3 mm
diameter tungsten carbide balls: 1.6 g of the above ribbon, 240 mg
of carbon black (commercially available from MMM Carbon, Belgium
under the trade designation SUPER P), 0.8 g of a polyimide coating
solution (commercially available from HD Microsystems, Cheesequake
Rd, Parlin, N.J. under the trade designation PYRALIN P12555 as a 20
weight percent solution in N-methyl-2-pyrrolidinone), and 4.2 g of
N-methyl-2-pyrroline (commercially available from Aldrich,
Milwaukee, Wis.). The milling vessel was placed in a planetary mill
(PULVERISETTE 7, available from Fritsch GmbH, Idon-Oberstein,
Germany) and the contents were milled at a setting of "3" for 1
hour.
[0093] After milling, the mixture was transferred to a notched
coating bar and coated onto a 15 micrometer thick copper foil as a
strip having a width of 25 mm and a thickness of 125 micrometers.
The strips were cured at 150.degree. C. under vacuum conditions for
2.5 hours to form an electrode. The electrode was then used to
construct 2325 coin cells having a 300 micrometer thick metallic
lithium foil counter/reference electrode, two layers of a flat
sheet polypropylene membrane separator (CELGARD 2400, commercially
available from CELGARD Inc., Charlotte, N.C.), and 1 M LiPF.sub.6
in a 1:2 mixture of ethylene carbonate and diethyl carbonate as the
electrolyte. The 2325 coin cell hardware is described in A. M.
Wilson and J. R. Dahn, J. Electrochem. Soc., 142, 326-332
(1995).
[0094] Electrochemical cells were cycled between 0.9 V vs. the
metallic Li/Li ion reference electrode and 5 mV vs. the metallic
Li/Li ion reference electrode at a constant current of 100 mA/g
(500 .mu.A) using a cell tester (Maccor Inc., Tulsa Okla.). The
current was allowed to relax to 10 mA/g (50 .mu.A) at the lower
voltage cutoff before the next charge cycle. The voltage versus
capacity curve is shown in FIG. 2. The reversible specific capacity
was 900 mAh/g.
Example 2
Si.sub.60Al.sub.14Fe.sub.8TiIn.sub.3Sn.sub.4(MM).sub.10
[0095] An alloy composition
Si.sub.60Al.sub.14Fe.sub.8TiIn.sub.3Sn.sub.4(MM).sub.10 was
prepared using a procedure similar to Example 1 by mixing 17.634 g
of silicon chips, 3.953 g of aluminum shot, 4.675 g of iron lumps,
0.501 g titanium sponge, 4.969 g tin shot, 3.605 g indium, and
14.663 g of mischmetal. The resulting melt-spun ribbon was annealed
by heating at 200.degree. C. for 2 hours under flowing argon. FIG.
3 shows the XRD pattern.
[0096] The resulting alloy composition was tested in
electrochemical cells as described in Example 1. An electrochemical
cell was prepared using the procedure described in Example 1. The
voltage versus capacity curve of this material is shown in FIG. 4.
The reversible specific capacity was 950 mAh/g.
Example 3
Si.sub.59Al.sub.16Fe.sub.8In.sub.1Sn.sub.6(MM).sub.10
[0097] An alloy composition
Si.sub.59Al.sub.16Fe.sub.8In.sub.1Sn.sub.6(MM).sub.10 was prepared
using a procedure similar to Example 1 by mixing 9.062 g aluminum,
34.785 g silicon, 9.379 g iron, 2.410 g indium, 14.949 g tin, and
29.414 g mischmetal. The melt spinning was at 1350.degree. C.
[0098] 10 g of the melt-spun ribbon was annealed for 2 hrs at
200.degree. C. in a tube furnace under a flow of argon. The XRD
pattern of the resulting alloy composition is shown in FIG. 5.
[0099] The following components were added to a 40 ml tungsten
carbide milling vessel containing two 10 mm diameter carbide balls
and ten 3 mm diameter tungsten carbide balls: 1.70 g of the above
melt-spun ribbon, 100 mg of SUPER P carbon (available from MMM
Carbon, Belgium), 1.0 g of a polyimide coating solution
(commercially available from HD Microsystems, Cheesequake Rd,
Parlin, N.J. under the trade designation PYRALIN P12555 as a 20
weight percent solution in N-methyl-2-pyrrolidinone), and 5.2 g of
N-methyl-2-pyrrolidinone (commercially available from Aldrich,
Milwaukee, Wis.). The milling vessel was placed in a planetary mill
(PULVERISETTE 7, commercially available from Fritsch GmbH,
Idon-Oberstein, Germany) and the contents were milled at a setting
of "4" for one hour.
[0100] After milling the solution was transferred to a notch
coating bar and coated onto a copper foil having a thickness 15
micrometers. The coated strip had a width of 25 mm and a thickness
of 125 micrometers. The coating was cured at 150.degree. C. under a
vacuum for 2.5 hours. Electrochemical cells were prepared as
described in Example 1. The voltage versus capacity curve is shown
in FIG. 6. The reversible specific capacity was 750 mAh/g.
Example 4
[0101] Lithium metal powder was made by chopping 150 micrometer
thick lithium foil repeatedly with a razor blade until the maximum
dimension of the individual particles were about 150 micrometers.
0.80 mg of the lithium powder was sprinkled onto a piece cut from
the cured electrode described in Example 1 containing 5.84 mg of
Si.sub.60Al.sub.14Fe.sub.8TiInSn.sub.6(MM).sub.10. The electrode
was then placed in-between two pieces of polyethylene film and
calendared by means of a hand roller. The resulting electrode was
assembled into an electrochemical cell versus a lithium counter
electrode as described in Example 1. The cell was cycled between
0.9 V vs. a metallic Li/Li.sup.+ reference electrode and 5 mV vs.
Li metal Li/Li ion reference electrode at a constant current of 100
mA/g using a cell tester (Maccor Inc., Tulsa Okla.). The voltage
versus capacity curve is shown in FIG. 7. The reversible specific
capacity was 650 mAh/g.
* * * * *